1. Field of the Invention
This invention relates to high power high temperature superconductive microwave circuits for various microwave devices and to a method of enhancing the power capability of such circuits.
2. Description of the Prior Art
High temperature superconductive (HTS) microwave devices enhance system performance with respect to noise figure, loss, mass and size compared to non-HTS devices. It is known to use HTS technology to design microwave components with superior performance (See Z. Y. Shen, "High Temperature Superconducting Microwave Circuits", Artech House Inc., Norwood, Mass., 1994; R. R. Mansour, "Design of Superconductive Multiplexers Using Single-Mode and Dual-Mode Filters", IEEE Trans. Microwave Theory Tech., Vol. MTT-42, pp. 1411-1418, July, 1994; Talisa, et al., "Low and High Temperature Superconductive Microwave Filters", IEEE Trans. Microwave Theory Tech., Vol. MTT-39, pp. 1448-1453, September, 1991; and Mathaei, et al., "High Temperature Superconducting Bandpass Filter for Deep Space Network", IEEE, MTT-S Symp. Digest, pp. 1273-1276, 1993). Typical microwave systems include high power as well as low power components but previous devices have concentrated on low power applications. Significant performance and economic benefits can be derived from the availability of both low power and high power HTS components.
For high power applications, the behavior of HTS thin films is quite different from that for low power applications. For example, surface resistance degradation and non-linearity have been observed in HTS microwave films operating at modest microwave power levels (See Fathy, et al., "Critical Design Issues in Implementing a YBCO Superconductor X-Band Narrow Bandpass Filter Operating at 77 K", IEEE, MTT-S Symp. Digest, pp. 1329-1332, 1991). The degradation and superconductive performances caused by the increased current density in the films as the power level is increased. When the current density reaches a maximum level, the power handling capability is limited to the power input at that level. The ability of an HTS microwave device, for example, an HTS filter, to handle high power levels is not only governed by the quality of the HTS materials but also by the filter geometry and its electrical characteristics. As better HTS materials are developed, the power handling capabilities of microwave components will increase.